Printing from bit map data in resolution of 600 by 600 dots per inch (dpi) generally provides excellent printing, particularly when slanted lines are smoothed by techniques which vary the actual printing slightly from that of the bit map along such slanted lines. This is achieved in some prior art printers by driving an optical printhead a selected number of times while it traverses the photosensitive surface an amount defined by one bit location of the 600.times.600 data. The laser printhead in such prior printers inherently illuminates the photosensitive surface to a height for one pel of the bit map (pel is believed derived from the term "picture element" and is used as the term for the unit of printing by dots or rectangles or similar units). The height for such a pel in a 300.times.300 resolution printer is 1/300 inch. The printer, however, can be controlled to illuminate eight contiguous rectangular slices as its light traverses the width of each 1/300 inch pel. That previous enhancement of resolution drives the laser in various permutations of those eight parts of the pel to achieve a final visual impression of smoothed slanted lines. In the preferred embodiment of this invention a laser printhead is used as just described except that the inherent height of its beam on the photoconductor is that for 600.times.600 resolution printing. The number of slices for which it can be controlled is unchanged from the foregoing 300.times.300 printer, and therefore four slices can be illuminated or not along the width of the area corresponding to a 1/600 inch width pel. In the preferred embodiment the higher resolution data is 1200.times.1200 dpi.
U.S. Pat. No. 5,109,283 to Carley, particularly with respect to FIG. 12A and FIG. 12B, assumes in its disclosure an optical system for printing in which the optical beam may be started and ended on a large number of boundaries while that beam is swept across a medium. In the embodiment the inherent height of the beam is 1/300 inch. Data at 600.times.600 dpi resolution is printed by printing a rectangle in variable widths within the area representing 1/150 inch in width to 1/300 inch in height at the approximate center of gravity and of the approximate same darkness of all of the bits in the 600.times.600 data.
In accordance with this invention, efficient printing avoiding high frequency off-and-on driving of the laser is employed which creates adjoining rectangular slices, not one variable rectangle at the center of gravity. The final printing by xerographic techniques is excellent.